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Old 2nd Jul 2023, 8:14 pm   #1
Laurence Smith
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Default Ekco U2 Wartime Civilian Receiver

I obtained this set from Facebook Marketplace back at the beginning of May and the seller had discovered it in an attic a few years ago. I’ve been after one of these for quite some time, so it’s good to have found one.

It is in nice original condition, with all the original paper capacitors still present with the only previous work I can see being the smoothing electrolytics, which are C17 and C18 on Trader sheet #688, having been replaced with grey Radiospares ones. The valves are all the original BVA marked types too. The inside of the base of the cabinet has the Gordon Russel ‘GR Ltd 1944’ makers stamp on it.

The mains lead was in a terrible state and the tuning drive cord had snapped. I have re-strung the dial with difficulty (it works, but there is still a bit of slippage now and again but this will have to do for now). Cold checks showed a healthy crack from the loudspeaker when measuring resistance across the primary of the output TX and the mains TX also showed continuity on all windings.

I replaced the mains lead and the grid coupling capacitor to the output valve. Powering up the set without the rectifier plugged in showed appropriate voltages from the secondary windings on the mains transformer and glowing heaters in V1,2,and 3. I then plugged the rectifier in and gradually wound it up on the variac with the lamp limiter in circuit over the course of a few hours. To my surprise, the set worked very well pulling in all the usual stations across MW with very good gain on R5L, Talksport and Lyca Radio and works very well for a short superhet.

Before powering up again I think it would be sensible to replace reservoir electrolytic C16 which appears original, as this is between the cathode of the rectifier and the centre tap of the mains transformer.

The speaker fabric on this example is thin brown nylon which I am now thinking is original, as I note that the two other Ekco examples at https://www.vintage-radio.com/recent...rtime-ac2.html and at post #22 at https://www.vintage-radio.net/forum/...=131040&page=2 both also have the same dark fabric, so I will try and find something similar in appearance to replace it with, as the existing fabric is badly damaged.
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Old 2nd Jul 2023, 9:25 pm   #2
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Default Re: Ekco U2 Wartime Civilian Receiver

What a lovely old set, and to think it saw service in WW2

Great that you are restoring it. Original valves as well, now that's good service life, you don't get that nowadays!
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Old 2nd Jul 2023, 9:50 pm   #3
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Default Re: Ekco U2 Wartime Civilian Receiver

It's in remarkably good condition for a set that's been recovered from an attic. When I was a kid this was our only radio and did sterling service.
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Old 2nd Jul 2023, 10:19 pm   #4
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Default Re: Ekco U2 Wartime Civilian Receiver

Very much Ekco knobs even if you hadn't given us the OEM code!
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Old 5th Jul 2023, 9:54 pm   #5
Laurence Smith
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Question Re: Ekco U2 Wartime Civilian Receiver

I have now replaced C16 and C10 and have been measuring a few voltages, and have found that the control grid of the output valve (BVA 266 aka EL33) has around 5.4v on it as measured on a DMM. I have read that this unwanted DC sometimes occurs due to inter-electrode leakage within the valve itself, so I tried a ‘sensibly equivalent’ KT61 borrowed from my HMV 1117 for comparison. I get exactly the same voltage reading on the grid with the KT61, which when working normally in the HMV has 33mV on its grid.

R10 which is the volume control that feeds the grid of the output valve has nearly doubled in value from 1M to 1.94M. This appears non-original, as is a Radiospares branded pot. There is also a 25k resistor between the volume control and the grid of the output valve which is not shown on the Trader Sheet, so perhaps this is unique to the Ekco chassis. I am suspecting that the high resistance of the volume control is likely to be the cause of the unwanted DC on the grid of V3 – would others agree with this?
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Old 5th Jul 2023, 10:17 pm   #6
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Default Re: Ekco U2 Wartime Civilian Receiver

C16 and C10 is meaningless to me without either knowing what they do in the circuit or having the circuit diagram that those part numbers relate to in front of me. Is either of them the grid coupling capacitor? If not, then this also needs to be replaced. There should not be that positive voltage on the control grid of the valve, so you'll need to find out why it's there.
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Old 5th Jul 2023, 10:42 pm   #7
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Default Re: Ekco U2 Wartime Civilian Receiver

Quote:
Originally Posted by Techman View Post
C16 and C10 is meaningless to me without either knowing what they do in the circuit or having the circuit diagram that those part numbers relate to in front of me. Is either of them the grid coupling capacitor? If not, then this also needs to be replaced. There should not be that positive voltage on the control grid of the valve, so you'll need to find out why it's there.
I replaced the grid coupling capacitor (C14) before powering up for the first time. C16 is the reservoir (obviously not relevant to the grid current issue) and C10 is V2 suppressor grid decoupling. I attach a snip of the relevant part of the circuit. C11 and C12 are low value (0.0001uF) which I would not expect to be causing trouble.

Thanks
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Old 5th Jul 2023, 10:43 pm   #8
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Default Re: Ekco U2 Wartime Civilian Receiver

Very nice to see, I hope things can be sorted out.
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Old 5th Jul 2023, 11:18 pm   #9
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Default Re: Ekco U2 Wartime Civilian Receiver

Try measuring V3 control grid voltage with respect to V3 cathode. You should then read a negative voltage on the grid. The anode and screen currents flow through R11 and R12, with the grid bias developed across R11.

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Old 6th Jul 2023, 12:24 am   #10
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Default Re: Ekco U2 Wartime Civilian Receiver

Quote:
Originally Posted by ronbryan View Post
Try measuring V3 control grid voltage with respect to V3 cathode.
Yes, I agree, now I see the circuit.
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Old 6th Jul 2023, 8:41 am   #11
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Default Re: Ekco U2 Wartime Civilian Receiver

Ron is right in Post #9. You should expect to see a positive voltage at grid 1 of the output valve when measured with respect to chassis. According to Trader Sheet #688 the combined anode and grid 2 currents flowing through the cathode for a brand new valve should be just under 29mA. That means a positive voltage between cathode and chassis of about 16v and a positive voltage between the junction of R11 and R12 and chassis of about 11v. It is the latter positive voltage with respect to chassis that you are measuring at the grid, via the volume control R10. You have actually measured about half this (5.4v according to your Post #5). I can think of 2 reasons why the voltage measured is low: first try replacing C13, 50uF electrolytic cathode bypass capacitor. It is probably leaky and/or has lost capacitance. Secondly the EL33 might have lost some emission and is therefore drawing a lower anode and/or grid 2 current than a brand new valve. It's also worth checking the EL33 grid 2 voltage (should be 175v). If lower then R15 might have gone high, or the rectifier is tired. The reason why the EL33 grid 1 voltage is positive with respect to chassis is to provide delayed automatic gain control (AGC) and to provide a small biasing potential on the Westector diode to keep it in conducting condition. Cheers, Jerry

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Old 6th Jul 2023, 4:36 pm   #12
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Default Re: Ekco U2 Wartime Civilian Receiver

Thank you for this post, I wish you every success with your restoration.

Whilst I have nothing to add technically nonetheless on a personal note your post brings back nostalgic memories of countless hours listening to the mellifluous tones of John Arlott commentating many a test match, Alvar Lidell reading the news, The Navy Lark, The Goon Show etc., etc., as one of these sets was given to me as a birthday present at age 11 when the 132kv National Grid circuit eventually reached our very small village. It went the way of all such items in the late 1960's, overtaken by the solid state age, I hope it gives you much pleasure.

Thank you again.
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Old 7th Jul 2023, 6:26 pm   #13
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Default Re: Ekco U2 Wartime Civilian Receiver

Thank you for all the nice comments and for the detailed technical advice.

The description of the circuit in the chapter on the WCR in Chas Miller’s Valve Radio and Audio Repair Handbook now makes much more sense to me.
So, the readings I quoted were taken with the lamp limiter still in circuit and there was 137v on G2 and -3.0v on G1 with respect to the cathode, which itself was at 8.5v WRT the chassis.

Taking the lamp limiter out of circuit, I get 153v on G2, -3.6v on G1 and 10v on the cathode.

R15 measured with one end disconnected from the circuit is a bit high at 2.95k. In terms of the C13 cathode bypass capacitor (25uF), I replaced this last week which made no difference to voltages and the original tests as above 20uF on my capacitance tester, so I have put it back in for now. It is actually a replacement itself, as I found wires from an earlier component at the solder joints, but is a Dubilier type with a cream coloured paper label so is pretty old.

I tried an old used Mazda UU5 instead of the original rectifier valve, and with this I get 175v on G2, 12v on the cathode and -4.2v on G1, which is mirrored by +4.2v at the junction of R11/R12 WRT the cathode. This is in line with what Chas Miller states in his book as ‘a shade over 4v’, so seems about right. I also get I get 7.8v between the junction of R11/12 and chassis and 245v HT. The gain of the set is much improved now too.

I’ve not restuffed wax capacitors before, but will do so with this set as I’d like to retain the original appearance of the chassis as much as possible. I will post further updates as the restoration progresses.

Thanks
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Old 19th Nov 2023, 4:37 pm   #14
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Default Re: Ekco U2 Wartime Civilian Receiver

I have now completed this restoration and have included some ‘after’ photographs below. I restuffed all the wax capacitors by heating each one, pulling the innards out and then inserting modern yellow polyester types and dripping candle wax into each end to seal them in. After I had restuffed C2 which is between the aerial coupling coils and chassis I had a brief panic as the radio hardly worked, which was traced to one of the fine wires attached to the aerial coils having come adrift. Re-attaching this restored normal operation. When I replaced the mains lead I chose not to earth the chassis and just used two core lead. When testing insulation between the primary winding of the mains transformer and chassis with a Megger, I get a reading of around 12 megohms on the 500v range. I’m not entirely sure what kind of reading is and isn’t acceptable here, but I’m thinking this is probably high enough to be acceptable.

In terms of the cabinet, I applied wax remover, wood reviver and finally a few coats of antique oil in the same way as described under the restoration detailed on this website at https://www.vintage-radio.com/recent...rtime-ac2.html The speaker fabric comes from a supplier that was recently recommended on this forum and I think although it is not like the original, it looks alright. Upon reassembly I found that the joint on one side of the base of the cabinet had partly come unstuck, so applied some wood glue which has worked well.

Overall, I’m quite pleased with the result as I’ve wanted one of these sets for a long time and now have nice example that I can display at home.
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Old 19th Nov 2023, 10:33 pm   #15
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Default Re: Ekco U2 Wartime Civilian Receiver

That's very nice to see, a few members here have restored Wartime Receivers.
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Old 21st Nov 2023, 3:41 pm   #16
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Default Re: Ekco U2 Wartime Civilian Receiver

Hello Laurence,

you have made a very good job of restoring your Ekco Wartime Civilian Receiver!
A few years ago I found one here in the Netherlands marked U32 on the chassis, a Kolster Brandes made example.
It had the same Radio Spares electrolytic capacitors fitted as in your set, in parallel with the original ones, which I have restuffed, using good quality modern ones.
The waxed paper capacitors have been restuffed as well, to keep the original under chassis look.
Nice to see you have done so as well, very rewarding to do.
A friend has used bees wax on the cabinet, that looks much better now.

Enjoy your very nice set!
With kind regards,
Desmond
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Old 22nd Nov 2023, 7:56 pm   #17
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Default Re: Ekco U2 Wartime Civilian Receiver

That looks very tidy now, good work!
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Old 24th Nov 2023, 5:45 pm   #18
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Default Re: Ekco U2 Wartime Civilian Receiver

In the circuit you show, it's likely C14 is leaky; it's the classic "that capacitor"

Just noticed you already did it. oops! Are voltages measured with respect to the chassis?

If you disconnect everything from the grid does it still show a voltage?

Derek

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Old 25th Nov 2023, 11:20 pm   #19
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Default Re: Ekco U2 Wartime Civilian Receiver

You made such a good job on those capacitors, it would be well worth including a note somewhere under the chassis to mention this for a future owner.
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Old 26th Nov 2023, 11:57 am   #20
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Default Re: Ekco U2 Wartime Civilian Receiver

Thanks for all the replies folks.

Derek - in my post #13 I was measuring the negative voltage of -4.2v on g1 of the output valve with respect to the cathode, which I understand to be about right. The final two readings quoted in that post showed 7.8v between the junction of R11/12 and chassis and the HT figure of 245v was also measured WRT chassis. I haven't tried disconnecting everything from the grid, but if I need to do any more work on the set I will try this and see what I get.

Stephen - In terms of the restuffed caps, I probably should have used a beeswax candle rather than a standard white one, as this would have looked more original. I'm still pleased with the result though.
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